1. Field of the Invention
The present invention relates to micro switches. More particularly, the present invention relates to Radio Frequency Micro-Electro Mechanical Systems (RF MEMS) micro switches, which use an electrostatic force for driving thereof.
2. Description of the Prior Art
In general, frequency separators (F/S's), field effect transistors (FETs), PIN diode switches, and so on, for high-frequency signal switches are used to control electric signals, e.g., for closing, restoring, and switching electric circuits in electronic systems.
However, drawbacks associated with the devices above include a low frequency separation degree in the F/S and a high insertion loss, low isolation, high power consumption, etc., in the semiconductor switches. Currently, micro switches for high frequency signals are used to make up for such drawbacks.
Micro switches for high-frequency signals are classified into resistively coupled (RC) switches and capacitively coupled (CC) switches based on a switching coupling method.
The micro switches are further classified into a cantilever type and a bridge type based on structural features of hinge parts thereof. The micro switches are also classified into a shunt-type and a series-type based on a high frequency signal switching method.
The operation principle of micro switches is to actuate hinge parts of a micro switch structure using electrostatic force, magnetostatic force, oscillation of piezoelectric element, and the like, as energy sources to turn signal terminal contact portions on and off. The micro switches are also classified into an electrostatic actuation type and a piezoelectric actuation type based on a driving method.
The conventional shunt-type micro switch described above has a structure in which signal terminals simultaneously play an electrode role of generating electrostatic forces, and input signal terminals and output signal terminals are connected to each other when the switch is in an off-state. Further, when the switch is in an on-state, a signal terminal and a ground terminal are short-circuited so that the output of an input signal is cut off. The shunt-type micro switch has a simple structure, but the switch suffers from a low isolation degree and on/off ratio.
The conventional series-type micro switch described above is a relay switch that completely separates input and output signal terminals from upper and lower electrodes generating an electrostatic force, in which, when the switch is in an off-state, the input and output signal terminals are completely disconnected so that an output for an input signal is cut off. Further, when the switch is in an on-state, the input and output signal terminals are connected so that an input signal is outputted. The series-type micro switch has a high isolation degree and on/off ratio, but drawbacks of the switch include a complex structure, a very difficult process, and a structure that is easily deformed.